It is well known that polymeric materials are generally considered useful as viscosification agents when dissolved in an appropriate solvent system. The major reason for this viscosity enhancement is due to the very large dimensions of the individual polymer chain as compared to the dimension of the single solvent molecules. Any increase in the size of the polymer chain will produce a corresponding enhancement in the viscosity of the solution. This effect is maximized when the polymer is dissolved in a "good" solvent. Therefore, in general, a soluble polymer is useful for thickening solvents, while a water soluble polymer is appropriate for increasing the viscosity of aqueous systems. With regard to aqueous solutions, solvent soluble nonionic polymers and high charge density sulfonated or carboxylate polyelectrolytes are quite useful in this regard and are commonly used materials. However, the solution properties of the former family of materials are controlled primarily through modification of the molecular weight of the polymer and through changes in the level of dissolved polymer. These materials become especially effective at concentrations where the individual polymer chains begin to overlap. This "transition" is commonly referred to in the literature polymer chains begin to overlap concentration or simply C*. It should be noted that in most nonionic polymers of commercial interest, a relatively large amount of polymer is required prior to reaching C*. Therefore, this approach is undesirable from an economic viewpoint. Moreover, the rheological properties of many of these nonionic systems have been published. The results of these studies shown that, in general, these solutions are shear thinning over all shear rates investigated.
Polyelectrolytes, on the other hand, are very useful and the most commonly used materials. However, the solution properties of these materials begin to deteriorate as low molecular additives (i.e., acids, bases or salts) are dissolved in the solution. These additives screen the charges that are fixed along the chain backbone which results in a decrease in the dimensions of the polymer molecule. The viscosity diminishes as long as the chain continue to shrink.
It has been found previously (U.S. Pat. Nos. 4,460,758 and 4,540,496), for example, that intrapolymer complexes, composed of a nonstoichometic ratio cationic and anionic monomeric units, can be useful in viscosifying aqueous solutions systems (as required in a variety of well control and workover fluids; i.e., water based drilling fluids and acid gelation systems). More importantly, these polymeric materials possess higher viscosity in acid, base or salt solution than in the corresponding fresh water system. Even more interesting is the observation that these polymeric materials show a corresponding viscosity enhancement as the concentration of the dissolved acid, base or salt is increased, even though the polyampholyte contains a substantial amount of dissociable charge. As explained earlier, these viscosity results are unexpected since the general tendency of charged macromolecules in these types of aqueous solutions shows a marked decrease in thickening efficiency.
Furthermore, in recent years, interpolymer complexes have received considerable attention in the literature due to their interesting and unique properties. In most instances, these complexes are formed by intimately mixing aqueous solutions containing high-charge density polyelectrolytes possessing opposite charge. When these polymer molecules meet in solution, the interaction between oppositely charged sites will cause the release of their associated counterions forming the complex. The counterions are now free to diffuse into the bulk solution. Normally, phase separation occurs upon prolonged standing in these high-charged density complexes. As a result, these materials have poor viscosification properties. In previous U.S. patents it is reported that low-charge interpolymer complexes are soluble and effective in viscosifying aqueous solution systems. More importantly, these complexes possess a substantially higher viscosity than the corresponding individual low-charge density copolymer components. As detailed earlier, these characteristics are unexpected since high-charge density complexes are insoluble in these conventional solution systems.
Even more interesting is the unique and unexpected result that these soluble interpolymer complexes are capable of enhancing the viscosity of aqueous solutions under relatively broad shear conditions. With these unique polymeric materials, dilatant behavior occurs in aqueous fluids which are of extreme technological utility. It is further noted that under the identical experimental conditions, the viscosity of the individual copolymer components show the normal shear thinning behavior.
Shear thickening fluids are rare and have mostly been demonstrated in suspensions. .sup.(1) Polymer solutions and melts are known, on the other hand, to exhibit strong shear thinning behavior, while most liquids of lower molecular weight are Newtonian. FNT .sup.(1) W. H. Bauer and E. A. Collins in "Rheology," Vol. 4, edited R. R. Eirich, page 459, Academic Press, 1967.
A polymer which was introduced by ICI (FM-9) as an antimisting agent for jet fuel was shown to be "progressively shear thickening." work done by S. T. J. Peng and R. F. Landel .sup.(2) at Jet Propulsion Laboratories under an FAA contract for antimisting in jet fuels showed that subjecting a solution of FM-9 in jet fuel at about 0.3-1.0 weight % polymer to steady shearing will produce viscous growth with time. It was found that the time scale and the extent of thickening can be accelerated by either increasing the concentration or by increasing the shear rate. The composition of FM-9 is not disclosed by ICI or by other agents working with this polymer. FNT .sup.(2) S. T. J. Peng and R. F. Landel, J. Appl. Phys., 52, 5988 (1981).
Peng and Landel correlate antimisting behavior with shear thickening or with high elongational viscosity which is exhibited by fluids that are able to demonstrate flow in a tubeless siphon. .sup.(3) FNT .sup.(3) S. T. J. Peng and R. F. Landel in "Rheology," Vol. 2, edited by G. Astarita, page 385, Plenum Press, 1980.
However, as previously noted, polymeric materials are useful as viscosity enhancers when dissolved in the appropriate solvent system. The principal reason for this behavior is due primarily to the large volume which a single macromolecular chain can occupy within the solvent. An increase in the size of the chain produces a concomitant enhancement in the solution viscosity. However, when the polymer chain is placed in a shear field, segmental orientation takes place in the direction of the shearing force. The viscosity of the fluid dramatically drops due to this orientation phenomena. This is a typical behavior of most solutions containing dissolved polymeric materials. However, if the polymer molecule has a high molecular weight with a relatively flexible backbone and the solvent viscosity is sufficiently high, different behavior is anticipated.
It has been shown by several groups .sup.(4) that with increasing shear rates the viscosity should show a decrease, followed by a minimum value and a subsequent increase in cases where both solvent viscosity and polymer molecular weight are very high. This latter effect gives rise to dilatant behavior. However, the above mentioned conditions required for the appearance of shear thickening behavior in these polymeric solution systems are not applicable for many technologically interesting fluids. In most of the common synthetic polymers, it is difficult from a synthetic viewpoint to obtain sufficiently high molecular weight and, in addition, most solvents (for example, water) have rather low viscosities. FNT .sup.(4) O. Quadrat, Adv. Colloid Interface Sci., 24, 45 (1985).
The instant invention teaches that a novel family of cationic-alkyl containing monomers, i.e. polymerizable moieties, form large structures in solution. The dimensions of these structures are comparable to those of polymeric chains. As a result, these structures, formed from these monomers are useful and very effective viscosifiers for aqueous solutions. In addition, these monomers have markedly unique and improved solution properties, as compared to conventional water soluble polymers. These fluids formed with these monomers can adequately be described as polymerizable cationic viscoelastic monomer fluids.
In addition, these monomers have markedly unique and improved solution properties in high brine environments, as compared to conventional water soluble polymers.
These monomers are based on, but not limited to, the incorporation of the above cationic monomers into an aqueous fluid system.
In addition, these monomers are not incorporated into a polymer chain structure via conventional synthetic techniques to form hydrophobically and associating type polymers. Very effective rheological control is assured even without the need to form a hydrophobically-associating polymer.
It should be noted in this regard that the use of hydrophobic groups on water soluble polymers to enhance the rheological properties of water based fluids has been described. One approach to provide polyacrylamide based systems containing hydrophobic groups is described by Bock, et al., U.S. Pat. Nos. 4,520,182 and 4,528,358. Water soluble acrylamide copolymers containing a small amount of oil soluble or hydrophobic alkylacrylamide groups were found to impart efficient viscosification to aqueous fluids. Landoll, U.S. pat. No. 4,304,902, describes copolymers of ethylene oxide with long chain epoxides which also required relatively large polymer concentration (approximately 1%) for thickening water and required surfactants for solubility due to irregularities in the polymerization. In a related case, U.S. Pat. No. 4,428,277, modified nonionic cellulose ether polymers are described. Although these polymers show enhanced viscosification relative to polymers not containing hydrophobic groups, the viscosification efficiency was very low, requiring 2 to 3 weight percent polymer to provide an enhancement. The use of surfactants to enable solubility and, in turn, viscosification, by a water soluble polymer containing hydrophobic groups is described by Evani, U.S. Pat. No. 4,432,881. The hydrophobic groups claimed are attached to the polymer via an acrylate linkage which is known to have poor hydrolytic stability. In addition, the need for a surfactant to achieve solubility and thickening efficiency should make such a system very salt sensitive, as well as very sensitive to small changes in surfactant and polymer concentrations. Emmons, et al., U.S. Pat. No. 4,395,524, teaches acrylamide copolymers as thickeners for aqueous systems. While these polymers possess hydrophobic groups they are prepared using alcohol containing solvent which are known chain transfer agents. The resulting polymers have rather low molecular weights and, thus, relatively high polymer concentrations are required to achieve reasonable viscosification of water based fluids.